Why bamboo? Well, it's soft, breathable, eco-friendly, apparently naturally anti-biotic, and supports nice peoples. What more could you want?
Well, in http://www.watermarkonline.com/ (in an article that appears to have broken in the past 3 days), Dan Jacobs, one of the owners, describes why he went into the business. (I'm paraphrasing here.) "I got a bamboo shirt online, and then I wore it to a party. And the whole night people kept fondling me, it was so soft. So we decided to open a store."
I'm rather happy with my shirt.